Pyelonephritic End-stage Kidney and Ureterocutaneous Fistula in a Shetland Pony

A 12-y-old Shetland Pony was presented with a mucus-secreting fistula in the right paralumbar fossa. Surgery was performed to unravel the origin of the fistula. The horse died under anesthesia and was forwarded to autopsy. The right kidney was markedly atrophic and fibrotic, consistent with unilateral end-stage kidney. The right ureter was markedly thickened, but with luminal continuity leading into the urinary bladder where a partial obstruction caused by nodular para-ureteral fat necrosis was evident. The lumen of the cutaneous fistula was continuous with the right ureter; therefore, we diagnosed the lesion as a ureterocutaneous fistula. Anomalies of the ureter are uncommon, and ureterocutaneous fistula formation in equids has not been reported previously to our knowledge.